The mechanisms of protein secretion and assembly into biological membranes will be studied by a combined biochemical and genetic approach. Trigger factor, a protein which catalyzes the folding of pre-secretory proteins into an assembly-competent form, will be purified and its mode of action characterized. It`s gene will be isolated and used to establish the physiological role of this protein. Translocation competent membrane vesicles will be solubilized with detergents and those proteins which are needed for secretion and membrane assembly will be isolated. Particular emphasis will be placed on illuminating the basis for two energy requirements for membrane assembly, ATP and the membrane electrochemical potential. In addition, we will characterize translocation poison sequences and hydrophobic helpers, two newly discovered elements within proteins which govern their membrane assembly.